A tour costs 7,50 euro per person.
The minimal costs for a group is 20 euro.
So, yes you can book the tour for 2 or even 1 person when you are willing to pay the minimum of 20 euro.
Sincere Thank You
I cordially want to thank You - UtrechUndergroun - for this initiative and Marc for an amazing tour. I'm happy to get to know you. Wish you all the best.